The present invention relates to matrix printing, i.e., to printing by means of composing a character from a multiple of dots; and more particularly, the invention relates to matrix print heads having a plurality of print wires or styli arranged in two or more vertical columns.
Matrix printers are widely in use today; their success is, no doubt, attributable to the fact that they constitute cost-effective, high-speed printers, the high speed being measured in relation to automatic typewriters, or the like. While satisfactory generally, the matrix printer is not usually regarded to be a high-quality printer, the term "quality" refering to the visual appearance of the printed characters. An improved appearance requires a larger number of print dots as well as a dot pattern in which dots are not juxtaposed but overlap. This feature, however, slows the printer down.
U.S. Pat. No. 3,757,346, for example, discloses a single column of wires or styli in the print head; and the wires are vertically displaceable through oblique, parallel guide slots for all of the needles. A particular and particularly controlled electromagnet serves as a drive for this displacement. A single column of styli is, however, detrimental and serves merely to reduce the number of styli. In the case of too few styli, the quality suffers.
German printed patent application No. 26 32 293 (based on U.S. patent application Ser. No. 600,985 of Aug. 1, 1978) suggests the use of a stationary column of styli next to a vertically displaceable one. The capability of vertical displacement serves for establishing a hybrid printer which combines: selective high speed or high quality. This known application describes also turning of the head about a horizontal axis. However, characters printed with a tilted head have inevitably a somewhat oblique appearance.